In general, both high grip performance and abrasion resistance are required of tread rubbers for high performance tires. Conventionally known rubber compositions having high grip performance include: rubber compositions containing styrene-butadiene copolymer rubber (SBR) with a high glass transition temperature (Tg); rubber compositions whose rubber component is loaded with process oil replaced with an equal amount of high softening point resin; rubber compositions highly loaded with softeners or carbon black; rubber compositions containing small particle size carbon black; and rubber compositions containing combinations of the foregoing components.
However, the use of SBR with high Tg can disadvantageously result in an increased temperature dependence so that greater changes in properties are caused by temperature changes, and also in significantly deteriorated processability. Moreover, if the replacement amount is high, the replacement of process oil with high softening point resin can result in an increased temperature dependence due to the presence of the high softening point resin. The use of small particle size carbon black or a large amount of softeners can cause drawbacks such as poor dispersion of carbon black and reduced abrasion resistance.
Patent Literature 1 proposes as a means to solve the above problems a rubber composition containing a partially hydrogenated low molecular weight styrene-butadiene copolymer. However, as described in this document, the degree of hydrogenation is limited because of bleeding of low molecular weight components.
It is thus difficult to improve abrasion resistance and grip performance while ensuring processability and bleed resistance. Moreover, abrasion resistance and grip performance are usually in a trade-off relationship. As described, at present, there is no technique to provide excellent abrasion resistance, grip performance, and durability of grip performance while providing good processability and bleed resistance. Therefore, such a technique is needed.